Elastomeric pumps are widely used in healthcare settings to deliver fluids and medication to patients. In some pumps, fluid is stored in a drug reservoir or bladder made of silicon or another rubber polymer and attached to a central support core. When filled, the bladder expands and the increased surface area of the bladder stores energy that exerts pressure on the fluid, driving the fluid out of the bladder. The flow rate of the fluid is often limited by a restricting orifice such as a glass capillary or a section of PVC tubing.
The symmetry and geometry of the bladder when filled affects the pressure exerted on the fluid therein and thus the flow profile of the fluid delivered from the pump. To constrain the expansion of the bladder, the bladder is often enclosed in an outer cover that restricts its asymmetrical expansion, such as a rigid cover or a flexible and non-expandable cover. In other types of pumps, the bladder is affixed to a sliding core, which helps to control the symmetry and geometry of the expanded bladder. In some pumps, the bladder is formed of a rubber polymer that exerts force on the fluid therein and a silicone lining on the inside of the bladder that prevents the fluid from coming into contact with the rubber polymer.